Have you physically checked your tyres for inside wear? It can be difficult to spot this on the ground, you will need to at least jack the car up and turn the wheels towards you and check them the whole way round with a torch. Also check for nails or foreign material embedded in the tyres as well. If the pitch changes with each gear change I would say it would be gearbox related. If it consistently changes with speed it does not rule out gearbox issues but it also brings in wheel bearing etc. Just because the bearings have recently been replaced does not rule them out. Could it be vibration from your break discs and pads? Vibrating noises can be difficult to find and may not originate from where you think.